Electromechanical transducer process

ABSTRACT

A method of manufacturing a device such as a resonant reed device having an enclosed mechanically displaceable conductive member with a controlled atmosphere within the enclosure, the method including steps of passing a substantial electric current through the member, the current being sufficient in magnitude to alter the mass of the member by the removal or addition of conductive material thereto or therefrom and measuring the displacement of a free portion of the conductive member while it is in motion in response to a predetermined force and thereby determining the mass distribution and inertial characteristics of the member while those characteristics are being altered within a sealed envelope containing a controlled atmosphere.

United States Patent 91 Stanish [54] ELECTROMECHANICAL TRANSDUCERPROCESS I [75] Inventor: Robert B. Stanish, Chicago, Ill.

[73] Assignee: Vibrionics Research Co., Lombard,

Ill.

[22] Filed: Nov. 13, 1968 [21] Appl. No.: 842,033

Related US. Application Data [60] Division of Ser. No. 417,108, Dec. 9,1964, which is a continuation-in-part of Ser. No. 193,520, May 9, 1962,Pat. No. 3,246,259.

[52] US. Cl. ..29/593, 29/622, 29/594, 29/595, 204/192, 204/208, 219/69V, 324/71, 316/13 [51] Int. Cl. ..G0lr 4/00, G05f 4/00 [58] Field ofSearch ..204/l92 R, 298 R; 29/622 R, 29/593 R, 594; 219/121 R, 69 V;324/71;

4/1962 Klingsporn .1: ..204/192x F EEOUEHCY SEQ/00020 1 Mar. 6, 1973Primary ExaminerRichard J. Herbst Assistant Examiner-Robert W. ChurchAttorneyPendleton, Neuman, Williams & Anderson [57] ABSTRACT A method ofmanufacturing a device-such as a resonant reed device having an enclosedmechanically displaceable conductive member with a controlled atmospherewithin the enclosure, the method including steps of passing asubstantial electric current through the member, the current beingsufficient in magnitude to alter the mass of the member by the removalor addition of conductive material thereto or therefrom and measuringthe displacement of a free portion of the conductive member while it isin motion in response to a predetermined force and thereby determiningthe mass distribution and inertial characteristics of the member whilethose characteristics are being altered within a sealed envelopecontaining a controlled atmosphere.

8 Claims, 6 Drawing Figures filed May 9, 1962, now US. Pat. No.3,246,259 and en titled AN ELECTRO-MECHANICAL TRANS- DUCER AND SYSTEMSRELATING THERETO. 1 There are many circumstances in the electronicsfield where it is desirable to convert mechanical motion into anelectrical signal. Many transducers have hereto- Another object of thisinvention is the provision of an improved oscillatory circuit havinggreatly increased signal capabilities while providing excellent waveform and minimum power inputs.

Still another object of this invention is the provision of a stableoscillator system having no active elements fore been proposed whichaccomplish this desideratum in various ways and with varying success.Typical of such devices adapted for static displacements are rotatableelements such as potentiometers and variable transformers, lineardevices such as sliding wires, tuned sections of wave guide or parallellines, and distortion sensitive devices such as strain gauges and thelike. For dynamic applications such as vibration analysis and the studyof resonant phenomenon vibrating reeds, contacts, and visual indicatorsare most common. Each of these devices has had impediments preventingunivers al use, the impediments including high cost, complexity, highpower requirements, the necessity of amplifiers and auxiliary equipment,lack of accuracy and the like.

The art' of motion and displacement measurement has developed greatly inrecent years with the development of computer analysis and the need foraccurate measurements which can be adopted readily for computer inputs.It is desirable that devices measuring accelerations, velocities ordisplacements render an electrical analog for immediate use in otherprocessing equipment.

There has been a particular need in the art for an inexpensive yetaccurate oscillatory device which can be tuned to a specific periodicfrequency and accurately control related circuits or provide a clearindication of the presence of a signal of the predetermined frequency.Such devices are useful in oscillators, frequency sensitive switches,decoding devices to sense a variable frequency code, frequencystandards,narrow band pass filters and frequency or period sensitive devices of 1all kinds where the variable is converted into a periodic electricalsignal.

The instant invention provides an improved system and apparatus tosatisfy all of, the foregoing needs. Itis one important object of thisinvention to provide'an improved transducer in which mechanicaldisplacement of a portion thereof alters an electrical signal which isdirectly related to the displacement. i

It is another object of this invention to provide an improvedelectromechanical transducer which is simplein construction, requires noelaborate equipment and is capable of producing a variable electricalcurrent directly related to the mechanical displacement-of an elementthereof.

It is still a further object of this invention to provide an improvedresonant device adapted to produce an electrical indication of theexistence of a predetermined periodic electrical or mechanicalphenomenon.

Another object of this invention is the provision of an the electrodeand. envelopefm' i it h' =,'I ="aj asw "provided in theldetaileddisclosureof this'speeification improved resonant system capable ofaccurately select ing a periodic signal having a single desiredfrequency and generating a control signal in response thereto whilerejecting other signals having only slightly different periodicity.

such as vacuum tubes, transistors or the like.

Another object of the invention is the provision of an improved resonantdevice employing a resonant element which can be tuned over a limitedrange.

Still another object of this invention is provision for driving aresonant element by utilizing electrostrictive units in mechanicalassociation therewith.

It is still another object of the invention to provide an improvedmethod for adjusting the vibratory characteristics of anelectromechanical transducer. I

It is still another object of this invention to utilize a heretofore'unappreciated characteristic of a device having a gas filled envelope,with spaced electrodes therein for producing an output dependent in partupon' the location of the electrodes within the envelope.

Another object of this invention is the provision of a method of tuningthe electrodes of agas' filled transducer by. passing an excessivecurrent therethrough.

Further objects of this invention will become manifest from aconsideration of this specification, the

accompanying drawings and the appended-claims. v In one form of thisinvention a small non'conductive cylindrical envelope is sealedwith twoelectrodes ex mally in motion,. or the two electrodesare securedtogether to eliminate motion of the two electrodes with respect to one.anothenlfthe two electrodes are both activated and are free forindependent movement, then they can be employed atindependentfrequencies'or, tuned, in'accordance with this invention, tothe same: I k

frequency. 1

While in one preferredform of the invention dis closed in detailhereinafteran electromagnetic device is employed to produce mechanicaldisplacement'of the electrodes with respect to the envelope be apparentthat othertechniques'could be iiiplo'yedf' although they may involveadditional mechanical linkages, seals and the like. Relamovementilbetwee moving: the electrode :or'the envelop two specificsystems employing the unique transducer, these systems beingcharacterized. by z'unexpected. and unforeseeable advantagesof'highJgai'n, simplicity; an

high frequency selectivity.However'many additional i a uses willimmediately occur to one skilled in t he art where the characteristicsof the instant transducer can be employed-to advantage.

' cipal vibratory characteristic of interest is the resonant frequency,although others, such as harmonic generation may also be affected.

For a more complete understanding of this invention, reference will nowbe made to the accompanying drawings wherein:

FIG. 1 is a longitudinal sectional top view of one em- 1 bodiment of theinvention;

FIG. 2 is a cross sectional view of the embodiment of FIG. 1; 1

FIG. 3 is a longitudinal sectional view of an alternate embodiment ofthe invention similar in many respects to the embodiment of FIG. 1;

FIG. 4 is a typical frequency response curve for the transducersillustrated in FIGS. 1-4;

FIG. 5 is a circuit diagram illustrating two systems employing theelectromechanical transducers shown in FIGS. 1-4; and

FIG. 6 is a circuit diagram illustrating one automatic technique andcircuit for practicing the method of this invention.

Referring now to the drawings, and more particularly to FIGS. 1 and 2,an electromechanical transducer 10 is illustrated including an openended cylindrical glass envelope 12 filled with an ionizable gaseousmedium 14 and sealed at one end with an appropriate plug 16 which mayalso be glass or any other gas impervious material which will form aseal with the material of which the envelope is made. Two electrodes 18and 20 are secured in the plug 16 and extend longitudinally into theenvelope 12. As shown clearly in FIGS. 1 and 2, at least the electrode20 is offset substantially from the longitudinal axis of the envelopel2, and is preferably quite close to a wall portion 22 of the envelope.While in the illustrated embodiment the electrodes extend substantiallythe entire length of the envelope 12 to a point adjacent the sealed end24, the precise length is not critical, the length of the elec- 'trodes18 and 20 being determined by the desired mechanical and resonantproperties thereof, and the length of the envelope being at leastsufficient to encase the electrodes.

In the event that both electrodes 18 and 20 are located adjacent thewall portion 22 then the resonant I characteristics of each must betaken into account, or

they must be constrained for unitary movement as described inApplication Ser. No. 193,520.

In the particular embodiment described the electrodes 18 and 20extend'through the end plug 16 to define two terminals 26 and 28 Theterminals are relatively short and rigid so that flexible conductors 30and 32 may be attached thereto -by 'any conventional technique such assoldering, wrapping or the like. The flexible conductors 30 and 32 maybe connected into a multiplicity of circuits, several of which will bedescribed hereinafter in substantial detail.

It is possible to obtain many of the advantages of this invention byproviding a single movable electrode 20 secured as a cantilever in theend plug 16. While a second conductor, in some form, is essential, itmay be secured along the surface of the envelope 12, preferably spacedfrom the wall portion 22, or it could be an aquadag or similarconductive coating on the nonconductive wall of the envelope 12. In anyevent it is quite significant that the fixed electrode be spaced awayfrom the movable electrode and also spacedaway from the adjacent wallportion 22 of envelope 12 for optimum output characteristics.

If only a single electrode is employed, or if only one electrode ismoved significantly then the periodic output will be dependent upon thevibratory characteristics of the principal electrode. A single resonantpeak as shown in FIG. 4 is thus produced. Also if two electrodes aredriven and are tuned in accordance with this invention, a single peakresponse curve will result, 0

and in general, the peak will be somewhat steeper than that of a singlemoving electrode. On the other hand if the two electrodes are driven butare not precisely tuned, then a broadened response curve or two distinct38 are disposed adjacent the wall portion 22 of the en-' velope l2 andthe core is so oriented that a magnetic flux field is generated whichwill include within its path at least the electrode 20. Thus by the lawsof magnetics, energization of the coil 36 will result in a field whichwill cause the two electrodes to be attracted toward the poles of core38. As it is preferred that the electrode 18 disposed outside of theeffective field of magnet 36, relative movement of electrode 18 isinsignificant, and substantially all of the movement of electrode 20will be normal to the envelope wall 22.

For the described embodiment to operate it will-be apparent that theelectrode 20 must be of a magnetically attractable material. In oneembodiment of the invention two steel rods are employed which areapproximately two inches long and 0.015 inch in diameter. In a secondembodiment two wires, each about one-half inch long and formed from0.010 inch Vibralloy stock gave excellent results. Vibralloy is an alloyformed of nickel and iron with about 9 percent molybdenum which has anextremely stable Youngs modulus for changing temperatures. Theelectrodes may be displaced by other techniques although magneticdeflection is the simplest and preferred. Electrostatic deflection couldbe employed, or with proper seals, mechanical linkage for externalmanipulation could be utilized. It is also possible, in the cases ofoscillatory phenomenon to use electrodes of substantial mass andphysically move the envelope, thus producing relative movement betweenthe envelope and the electrodes as a result of the inertia of theelectrodes. This will be described in detail with respect to FIG. 3.

In the preferred embodiment of the invention the envelope 12 wasevacuated and then filled with neon gas.

It was found that the device operated over a wide range of gas pressuresand the optimum gas pressure appears to be dependent upon the otherphysical characteristics of the design including the spacing of theelectrodes, the diameter of the envelope and the position of theelectrodes with respect to the adjacent envelope wall 22. Substantialoutputs are produced for example when pressures haye also proven highlysatisfactory. For example, devices having envelope diameters of only afew millimeters, such as the NE 2 type neon bulb have proven verysatisfactory with gas pressures over a range including 15 mm. and 30 mm.(hg). However, the tuning techniques to be described are generallybetter applied to the devices employing lower gas pressures. While neonappears to be the most desirable gaseous medium because of itsavailability and low cost, any ionizable medium including krypton,argon, xenon and the like, or mixtures of various gases may be employed.

It is obvious that the artisan must relate the physical dimensions ofthe various components to the gas characteristics to optimize output andlinearity of the device. I

An alternate embodiment of the invention is illustrated in FIG. 3. Theoperation and construction are substantially the same as alreadydescribed with respect to FIGS. 1 and 2. The envelope 12 has one closedend 24, the other end being closed by an appropriate seal-,

ing plug 16. The cavity is charged with an appropriate ionizable gassuch as neon. In the embodiment of FIG. 3, however, the electromagnet 36is replaced with an electrostrictive device 40 secured to the glassenvelope 12 with anlappropriate cement 42. An epoxy or similar cement iswell suited to this use. The electrostrictive device 40 may be of anywell-known type, or can be replaced with any other device capable ofvibrating the envelope 12. The preferred device is a multiple layerbarium titanate transducer. One such device shown as Multimorph is wellsuited to this use. Devices of this general type are described in US.Pat. No. 2,478,223 entitled Electrostrictive Translator. Theele'ctrostrictive device vibrates the envelope transverse to theelectrode axis and thus relies upon inertia of the electrode to producerelative motion. The device 40 may be energized through a pair of leads44 and 46.

The circuit diagram of FIG. 5 illustrates two important and unique usesof the transducers described above. The single circuit is adapted foruse as a stable oscillator and as a frequency sensitive or frequencyresponsive unit. The mode of operation is determined by the position ofthe switch 48. As shown in FIG. 5a

double pole double throw switch including switch section 48 is in theupper position whereby the circuit is connected as an oscillator. Whenswitch 48 is thrown to the lower position the circuit is adapted for useas a frequency sensitive device, filter, or decoder. The

be considered as the primary winding, has one terminal connected to oneelectrode of the transducer 10. The

other electrode of the transducer 10 is connected to the 1 ground 50.

A potentiometer 60 is connected across a potential source such asbattery 62 and one common connection of the battery and potentiometer isconnected to ground 50. The wiper of potentiometer 60 is connectedthrough a resistor 64 to the transformer winding 58. A capacitor 66 isconnected across the corresponding terminals of the windings 52 and 58for damping and filtering. With the foregoing arrangement of components,closure of switch 48 produces a small current in electromagnet winding36 which attracts the electrodes within the transducer 10. Movement ofthe electrodes within the transducer results in a change in the currentthrough the transducer, and consequently a change in the current intransformer winding 58. This change results in additional current in thetransformer winding 52 which in turn further energizes the electromagnetwinding 36. Thus, in accordance with the well'known principles ofoscillating circuits the electrodes move in one direction to the limitsof the availabletravel, and thereafter the current through theelectrodes tends to stabilize and consequently the current in thetransformer winding 52 diminishes, resulting in reduced flux in theelectromagnet winding 36 and return of the electrodes to the relaxedposition. This phenomenon repeats with a periodicity principallydependent upon the resonant characteristics of the electrodes.

The foregoing oscillator circuit has been found to be extremely stableand reliable in use. It produces good waveform for all normal operationand is stable for changes in temperature, operating voltages, and othercircuit characteristics over wide ranges of values.

When the switch 48 of FIG. 5 is thrown to the lower position a signalcontaining randomor coded frequencies may be applied at the inputterminals 74 and 76. Terminal 76 is connected to ground 50 and terminal74 is connected through switch 48 to theelectromagnet winding 36.Winding 36 will thus be energized with any signal applied thereto, butbecause of the mechanically resonant character of the electrode, theelectrode will remain substantially non-responsive .to all but thefrequency to which they are tuned. At the resonant frequency of the reedor electrode the motion will be substantial, producing very substantialvariations in the current flowing in the circuit which includes theelectrodes, the transformer winding 58, resistor 64 and the combinationof potentiometer 60 and battery 62.

An output terminal 68 is connected to transformer winding 52 by thesecond pole associated with switch 48 and thus winding 52, in thisconfiguration becomes an output or secondary winding. The output atterminal 68 varies with frequency in accordance with curve 78 of FIG. 4and thus this is a chart of quality or circuit 0. As is apparent fromthe curve, the circuit has a relatively high equivalent Q, and is thushighly frequency selective. In the embodiment described where theresonant frequency is about 266 c.p.s., indicated by solid line 72, thehalf power points, in-

dicated by broken lines 80 and 82 occur at about 264 Transducers havebeen constructed in accordance with this invention having resonantfrequencies in the range of 200 to 3,000 cycles. However, this does notestablish a limitation upon the frequency range as both higher and lowerfrequencies can be provided, if desired. By carefully selecting thecomponents of the transducer and exercising normal care in manufacture,it is possible to design the transducer with a predetermined resonancevalue. However, because of. the tolerances of manufacture and the high Qcharacteristics of the transducer, it is highly desirable to tune eachtransducer as a final manufacturing step. The necessity of selectingmatched pairs or groups is thus eliminated.

In accordance with this invention, each transducer may be tuned or itsresonant and vibratory characteristics altered in a unique manner. Ithas been found that a current may be passed between the two electrodesor conductors of a sufficient magnitude that a metallic depositionoccurs. The current is nevertheless below the value at which anypermanent destructive effects are produced in the glass envelope, gas,or other components. In general, the current, preferably unilateral,which best accomplishes the metallic transfer is approximately ten timesthe normal operating current for the transducer. Thus, in one typicalembodiment, the normal operating current is 300 microamperes whiledesirable metal transfer occurs at 2.5 to 3.5 milliamperes;

It has been observed that at relatively low metal transfer currents, theaction appears to concentrate near the free end of the electrodes andfor increasing current the transfer involves a greater portion of thebody of the electrodes. It has also been observed that the cathodeexhibits a loss of mass while the anode exhibits a slightly reducedincrease in mass. The difference in the two mass changes is the resultofsome metallic deposit upon the inner glass wall and other bodies withinthe envelope. It appears that the metal transfer is principally theresult of the bombardment of the'cathode with positive ions which inturn dislodge small metallic particles from the cathode which aredeposited on the anode and inner envelope walls.

In one typical embodiment of the invention employing a electrodes, ithas been found that a metal transfer current of 3.5 Ma. produces afrequency change at the cathode of 10 cycles per second per hour oftransfer. An automatic circuit for accomplishing the adjustment offrequency by altering the mass characteristics of the cathode isillustrated in FIG. 6. Therein, a transducer 10a is being tuned to apredetermined frequency by driving one of its electrodes 20a from afrequency standard 84. The output of frequency standard 84 is applied tothe electromagnet including pole piece 38a and coil 36a. In practice,the coil and pole piece are preferably secured to the glass envelope 12ato form an integral unit. Also in mounting the transducer both forcalibration and use, it is preferable to shock mount the glass envelopeand motive device together to mechanically isolate'them from theirenvironment. It has been found in practice that mounting the completeunit only on its terminal wires which are selected to have the desiredresiliency, excellent shock mounting and mechanical isolation result.

The frequency standard may be any well known device provided it has astable output of a fixed frequency and preferable with a sinusoidal waveform. Various audio frequency generators are available with the requiredcalibration and stability. 7

The electrodes 18a and 20a are energized from a DC supply 86,illustrated as a battery merely for con-' venience. The negative supplyterminal is connected to the electrode 20a which is closest to thedriver, and

closest to the glass envelope 12a. The positive terminal of supply 86 isconnected through a current meter 88, a normally closed switch 90 inparallel with resistor 122, and a current controlling variable resistor92 to the more centrally located electrode 18a. The resistor 92 isadjusted to provide the required current through the transducer formetal transfer and consequent mass al teration. As mentioned herein, inone embodiment of the invention a current of 3.5 Ma. was employed forthis purpose.

As the frequency standard 84 is driving the electrode 18a, the currentthrough the transducer 10a will have an A.C. component in accordancewith the teaching of this invention. That A.C. component is coupled tothe grid of an amplifier triode 94 through a capacitor 96 and a resistor98. The grid of amplifier 94 is returned to ground through grid resistor100. Cathode bias for amplifier 94 is provided by the cathode networkincluding resistor 102 and capacitor 104.

, The output of amplifier 94 is taken at the plate and applied throughcapacitor calibrating resistor 106 and relay coil 108 to groundQThe D.C.return for amplifier 94 is through resistor 112 and power supply 114 toground. As already discussed above, the power supply 114 is shown ascomprising a battery; however any well regulated power supply will provesatisfactory.

Relay coil 108 is provided with a buffer capacitor 116 and ismechanically arranged to open normallyclosed contact 90 and to closenormally-open contact 118. Opening contact 90 places resistor 122 inseries with variable resistor 92 and thus reduces the current throughtransducer 100. Resistor .122 is selected to produce a current throughtransducer 10a which is less than thatrequired for metal transfer andthe device will operate in its normal mode. In the typicalembodimentdescribed above, this would be approximately '350 microamperes. Theenergization of coil 108 will also close contact 118 which is in serieswith an indicating lamp 120 which is energized by the supply 1 14.

In the described system, the transducer 10a will initially have aresonant frequency below the predetermined frequency as established bydriver 84. As the electrode 200 is the cathode, its mass will be reducedand its resonant frequency raised as already discussed. The outputvoltage appearing across resistor 100 will follow the curve of FIG. 4.As the mass is altered and the resonant frequency of electrode 20aapproaches the driver frequency, the A.C. voltage will rise rapidly to alevel where relay coil 108 actuates switches 90 and 1 18. At this pointmass alteration is terminated.

Because the transducer was substantially overdriven by supply 86, thereduction in unilateral current will not produce a proportional decreasein A.C. signal. Furthermore, the hysteresis provided by relay coil 108should be sufficient to maintain actuation following removal of thesubstantial D.C. componenLIf the circuit exhibits any hunting oroscillatory effects they may .be ,eliminatedreadily by utilizing holdingcontacts with respect to coil 108.

' As will be apparent, the transducers 10 may thus be automaticallytuned to form high 0 devices having a very narrow frequency response toa frequency automatically adjusted to within a few cycles of thedesideratum.

While several specific embodiments of the invention have been describedin some detail, other systems using the unique transducer andmodifications of the transducer will immediately occur to one skilled inthe art. it

appears that the unusual characteristics observed in this invention area result of variable current flowing an electrode to a wall such as thewall of envelope 12. As the electrodes move toward the glass wallportion 22 the current will change'or vary. While a non-conductive wallis preferred, it appears that the effect is also present when the wallis conductive. It is probable thatthis phenomenon is the result of theprogressive variation and reconstruction of the plasma, space charge orion field which surrounds the electrodes during conduction.

The effect may be produced by placing the moving electrode or electrodesclose to the envelope as described above or an equivalent wall may becreated through the use of auxiliary devices. Included among theauxiliary devices contemplated are mechanical devices such as anon-conductive 'wall or barrier mounted within the envelope andelectrical devices such as arigidly mounted biased electrode to createan effective electrical wall.

' It has been found that the gas within the envelope should becontinuously ionized for best results and thus it is necessary toprovide a sufficient voltage between the electrodes to insureionization, but a limited current to prevent arc discharge in normaloperation. In the described embodiment a voltage of 400 volts in source62 with a one megohm potentiometer 60 connected thereacross was foundsatisfactory. It appears that with these parameters and the gas andcircuit parameters given above the space charge around the electrodes iseffectively altered by motion toward the envelope wall in such a mannerthat the current is reduced in a generally linear manner. The output issubstantially sinusoidal irrespective of the nature of the periodicinput.

Thevvariations are very substantial and enable the construction ofsimple circuits with low or negligible power requirements such as thosedescribed above. Nevertheless the circuits are capable of verysubstantial outputs. The current variations are produced by physicalmovement of the electrodes that is so slight that it is sometimesimperceptible to the unaided eye. Thus the device is capable ofsubstantially higher operating frequencies than have heretofore beenassociated with the more inexpensive mechanical resonators.

Without further elaboration, the foregoing will so fully explain thecharacteristics of my invention that others may, by applying currentknowledge, readily adapt the same for use under varying conditions ofser vice, while retaining certain features which may properly be said toconstitute the essential items of novelty involved, which items areintended to be defined and secured to me by the following claims.

I claim:

1. The method of manufacturing a device having an enclosed mechanicallydisplaceable member comprising the steps of:

a. providing an elongate resilient member having an electricallyconductive portion;

b. providing a body having a cavity therein;

c. mounting an end portion of said resilient member on said body with anopposite end portion comprising a free end within said cavity;

d. providing a conductor within said cavity spaced and electricallyisolated from said resilient member;

. controlling the atmosphere within said cavity;

. passing a predetermined electric current between said resilient memberand said conductor which is of sufficient magnitude to alter a portionof the mass of said resilient member; v

. measuring the displacement of said free end while in motion from arest position in response to a force; and

h. reducing said current to a level below that'at which said mass isaltered when the measured displace-ment in response to a preselectedforce is at a predetermined level.

2. The method of claim 1 including the step of vibrating the member witha predetermined periodicity while measuring the displacement thereof.

3. The method of claim 2 wherein said cavity. is filled with anionizable gas.

4. The method of claim 3 wherein said current is reduced below the levelat which said mass is altered and is maintained at a level above thatnecessary to ionize said gas.

5. The method of claim 4 wherein said member is a conductive cantilevermember having a fixed portion and a movable portion and the member andconductor are relatively positioned whereby the mass of the movableportion of said member adjacent said free end is reduced to therebyraise said resonant frequency.

6. The method of claim 1 wherein said measuring occurs simultaneouslywhile passing said electric current between said member and saidconductor.

7. The method of claim 6 wherein said current is automatically reducedin response to said measuring step when the displacement is at saidpredetermined level.

8. The method of claim 1 wherein said electric current includes a directand a periodic component and said measuring step comprises measuringsaid periodic component while displacing said member and including thestep of reducing said direct component of current below the magnitude atwhich said mass is altered when said measured displacement is at apredetermined level.

UNITED STATES PATENT OFFICE CERTIFICATE I CORECTION mmune, 3,71s 970Dated March6, 1973' mam ROBERT B0 STANISH It is certified that errorappears in the above-identifiedpatent and that said Letters Patent arehereby corrected as shown below:

Column 1', before line 2, insert This invention relates to an improvedelectromechanical transducer and circuits and apparatus-aassociatedtherewith. More particularly this invention relates to a transducerincluding a a mechanically displaceable element capable of generating avariable electrical phenomenon directly related to the displacementthereof whereby the transducer may be employed in unique systems relyingupon such phenomenon. Column 5, line 39, "shown" should read knownColumn 7, line 47, before "electrodes", cancel "a" and insertiron-nickel molybdenum should read placement-- In the references,"Waysmouth" should read Waymouth Signed and sealed this 22nd day ofJanuary 1974.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. RENE D. TEGTMEYBR Attesting Officer Column 10,line 30, "place-ment" Acting Commissioner of Patents

1. The method of manufacturing a device having an enclosed mechanicallydisplaceable member comprising the steps of: a. providing an elongateresilient member having an electrically conductive portion; b. providinga body having a cavity therein; c. mounting an end portion of saidresilient member on said body with an opposite end portion comprising afree end within said cavity; d. providing a conductor within said cavityspaced and electrically isolated from said resilient member; e.controlling the atmosphere within said cavity; f. passing apredetermined electric current between said resilient member and saidconductor which is of sufficient magnitude to alter a portion of themass of said resilient member; g. measuring the displacement of saidfree end while in motion from a rest position in response to a force;and h. reducing said current to a level below that at which said mass isaltered when the measured displace-ment in response to a preselectedforce is at a predetermined level.
 1. The method of manufacturing adevice having an enclosed mechanically displaceable member comprisingthe steps of: a. providing an elongate resilient member having anelectrically conductive portion; b. providing a body having a cavitytherein; c. mounting an end portion of said resilient member on saidbody with an opposite end portion comprising a free end within saidcavity; d. providing a conductor within said cavity spaced andelectrically isolated from said resilient member; e. controlling theatmosphere within said cavity; f. passing a predetermined electriccurrent between said resilient member and said conductor which is ofsufficient magnitude to alter a portion of the mass of said resilientmember; g. measuring the displacement of said free end while in motionfrom a rest position in response to a force; and h. reducing saidcurrent to a level below that at which said mass is altered when themeasured displace-ment in response to a preselected force is at apredetermined level.
 2. The method of claim 1 including the step ofvibrating the member with a predetermined periodicity while measuringthe displacement thereof.
 3. The method of claim 2 wherein said cavityis filled with an ionizable gas.
 4. The method of claim 3 wherein saidcurrent is reduced below the level at which said mass is altered and ismaintained at a level above that necessary to ionize said gas.
 5. Themethod of claim 4 wherein said member is a conductive cantilever memberhaving a fixed portion and a movable portion and the member andconductor are relatively positioned whereby the mass of the movableportion of said member adjacent said free end is reduced to therebyraise said resonant frequency.
 6. The method of claim 1 wherein saidmeasuring occurs simultaneously while passing said electric currentbetween said member and said conductor.
 7. The method of claim 6 whereinsaid current is automatically reduced in response to said measuring stepwhen the displacement is at said predetermined level.